A recent experiment that aims to deeply investigate the Solid Electrolyte Interphase (SEI) in a Lithium-ion battery, was conducted by researchers from the Department of Energy’s Oak Ridge National Laboratory (ORNL). Using a sophisticated process known as Transmission Electron Microscopy (TEM), the research is considered a major success relevant to the improvement of the battery’s overall performance and life.
Time-lapse Image of SEI Formation
Image Source: Science Daily Website
Purpose of the Research
According to the researchers, the main objective of this experiment is to shed light on the long-time debated issue on SEI’s dynamics, structure and chemistry during electrochemical cycling. Due to the unavailability of equipment capable of analyzing the battery electrode materials in their natural liquid state in recent decades, scientists’ effort of unlocking this obstacle has been made possible – with the aid of TEM technology.
But what exactly is SEI and why is this enigmatic phenomenon in Li-on and other batteries of high interest not only to ORNL but also to the Research and Development groups of many battery manufacturers?
Solid Electrolyte Interphase (SEI)
Solid Electrolyte Interphase (SEI) is a solid, dense and stable layer of oligomers and inorganic crystals formed on the surface of the negative silicon electrode during the initial charging of a lithium-ion battery. SEI results from the decomposition of organic solvents such as lithium and ethylene carbonate that are used as electrolyte solutions in batteries. One of the well-defined functions of SEI is that it prevents the further decomposition of electrolyte after the second charging. In the experiments conducted in ORNL, SEI is described as a nanometer-scale film, snowflake form, and resembles a dendritic (tree-like) pattern – descriptions possible to achieve because of the TEM equipment and the in situ (examining the electrochemical phenomenon in place where it occurs) experimental approach.
SEI Formation During Battery Charging Cycle
Image Source: MIT Technology Review Website
The prime interest of understanding the nature and composition of SEI is due to the fact that a range of a battery’s characteristics are highly dependent on its quality. This includes performance, irreversible charge loss, rate capability, cyclability, and safety.
Focus and Direction of Research Findings
The use of TEM that enables researchers to capture the moving image of the SEI formation process in real-time and nanoscale resolution makes this science experiment one of a kind – it has never been done before (click here to watch the video). According to the researchers, “this study brings us one step closer to understanding SEI formation and growth.”
What could be next is the focus to further improve the efficiency of lithium-ion batteries specifically on the ionic transport, alloying kinetics, and electron transport at the surface of the silicon electrode – electrochemical processes and mechanisms occurring at a nanoscale level. Furthermore, researchers will soon apply these techniques to studying different types of rechargeable and single-use battery electrodes and electrolytes and other energy storage systems like fuel cells.
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Infographic: Lithium-Ion battery